1. Field of the Invention
The invention relates in general to an image reading apparatus and an optical module thereof, and more particularly to an image reading apparatus being dust-proof, and an optical module thereof.
2. Description of the Related Art
In addition to a scanner, the present commonly used image reading apparatus includes a digital photocopy machine and a multi-function printer (MFP) with scan function. In terms of the ways documents are scanned, the image reading apparatuses can be classified into the flatbed type, where the documents are still when being scanned, and the sheet-fed type, where documents are moving when being scanned. No matter whether the former or the latter type of the image reading apparatus is used, the image reading apparatus acquires the image of the documents through a scan window. If dust particles adhere to the scan window, the images obtained by the scan apparatus will be affected. Take a sheet-fed scanner as an example. Referring to FIGS. 1A and 1B, a partial schematic diagram of a conventional sheet-fed scanner and an exploded view of the scanner of FIG. 1A are respectively shown. As shown in FIGS. 1A and 1B, a sheet-fed scanner 1 includes a casing 10, an optical module 11, an upper plate 12, window glass 13 and a document-feeding device 14. The document feeding device 14 and the window glass 13 are both disposed on the upper plate 12. The optical module 11 is fixed in position in the casing 10 and facing the window glass 13. The document-feeding device 14 is for transporting a to-be-scanned document across the window glass 13 of the upper plate 12 such that the optical module 11 can read the images of the to-be-scanned document.
As shown in FIG. 1B, when the upper plate 12 is disposed on the casing 10, owing to a gap that exists between the upper plate 12 and the casing 10, dust particles will enter the casing 10 from the exterior via the gap. If the dust particles are attached to the window glass 13, the images generated will be greatly downgraded. Referring to FIGS. 1C and 1D, FIG. 1C is a schematic diagram of the scanner scanning a document and FIG. 1D is a schematic diagram of the image generated by the scanner of FIG. 1C. If the dust particles are attached to the upper surface of the window glass 13, the user can easily clean them out. However, as shown in FIG. 1C, if the dust particles (such as P1 and P2) are attached to the lower surface of the window glass 13 and located right on the scan line S of the optical module 11, when the to-be-scanned document A moves in the direction D and passes the window glass 13, the dust particles P1 and P2 will result in unexpected lines L1 and L2 on the image generated by the optical module 11 as shown in FIG. 1D.
In order to clean the lower surface of the window glass 13, normally, the scanner has to be taken apart before the cleaning operation, which is very inconvenient for the user. If the dust particles attached to the lower surface of the scan window are not cleaned out, the optical module 11 will scan the dust particles attached to the scan window 13 along with the to-be-scanned document A and the dust particles become a part of the scan image of the to-be-scanned document A.